Variable transformer



May 23, 1961 F. I. ELLIN ETAL VARIABLE TRANSFORMER Filed Oct. '27, 19582 Sheets-Sheet l 45 J64 INVE Muff am/ //%S May 23, 1961 F. I. ELLIN ETALVARIABLE TRANSFORMER Filed Oct. 27, 1958 2 Sheets-Sheet 2 INVENTORS.1554c United States Patent Ofiice 2,985,857 VARIABLE TRANSFORMER FiledOct. 27, 1958, Ser. No. 769,696 7 Claims. (Cl. 336-148) This inventionis concerned with a transformer, more particularly a variabletransformer of the single winding or auto transformer type.

Variable transformers of the type disclosed herein are known in the artand generally include a winding energized with a predeterminedalternating current voltage. A sliding tap connected to an outputterminal then picks off a voltage anywhere from zero on up to thepredetermined energizing voltage, or even slightly higher if connectionsare properly made. Such transformers are widely used in laboratory testequipment, in power supplies, in filament controls, in speed control ofmotors, and in other installations. In many instances the sizerequirements of such transformers are severely restricted by the spaceavailable. This, in turn, limits the outputcurrent that can be drawn.

It is an object of this invention to provide a variable transformerhaving a higher output rating for anequivalent size than any heretoforecommercially available.

-It is a further object of this invention to provide a variabletransformer which is simple and economical to manufacture.

It is another object of this invention to provide a variable transformerwhich is rugged, positive in operation, and yet of simple construction.

Other and further objects and advantages of the present invention willbe apparent from the following description when taken in connection withthe accompanying drawings wherein:

Fig. 1 is a side view 'Fig. 2 is a rear end right of Fig. 1;

Fig. 3 is a longitudinal sectional view as taken along the line 3-3 inFig. 2;

Fig. 4 is an exploded perspective view of the shaft assembly;

Fig. 5 is a cross-sectional view as taken along the line 55 in Fig. 3;

Fig. 6 is a plan view of the transformer base;

ig. 7 is a perspective view of the transformer base;

Fig. '8 is a perspective view of an end cap utilized in conjunction withthe base; and

:Fig. 9 is a detail sectional view of a part of the end cap as takensubstantially along the line -9--9 in Fig. 8.

Referring now in greater particularity to the drawings, there will beseen a variable transformer generally indicated by the numeral 20. Thetransformer includes the usual magnetic core 22 comprising a spirallywound strip of transformer steel. Insulating material 24 is providedabout the outer circumference of the core, and similar insulatingmaterial 26 is provided about the inner circumference. A certain amountof insulating paper also is applied to one end of the core as indicatedat 28. A front end cap 30 and a rear end cap 32 are cemented to the endsof the core. The two end caps are substantially identical, and the rearend cap 32 is shown in perspective in Fig. 8. The end caps are molded ofphenolic plastic or the like, and with reference to Fig. 8 it will be ofthe transformer; view thereof as taken from the substantially 2,985,857Patented May 23, 1961 seen that the rear end cap includes a flatring-like body section 34 having a central aperture 36. As may be seenfurther with reference to Fig. 9, it will be apparent that the edge ofthe aperture 36 is bevelled and is provided with serrations 38 forpositioning the transformer winding 40 thereon. The rear end cap isprovided with a thickened rim 42. The rim is interrupted at 44, and apair of spaced apart projections 46 extends substantially radiallyinwardly on each side of the interruption. In the case of the rear endplate, a brass terminal 48 having a central threaded aperture 50 ismolded in place between the projections 46 and a short distance in fromsimilar shaped projection of plastic being provided in the circumferenceof the ca The front end cap is identical with the rear end cap, butlacks the insert 48, a place thereof. The threaded aperture 50 in theinsert 48 extends completely through the insert, and the insulatingsection 28, which conveniently may be cemented to the rear end caprather than to the core, is provided to prevent a mounting screw 52 fromengaging the core.

Following cementing of the end caps to the core the wire 40 is woundthereon substantially from the outside of one of the projections 46 tothe outside of the other projection, the wire extending through thecentral apertures 36 of the end caps and through the bore of the core,and being wrapped around the outside and ends of the core. Theserrations 38 position the wire at the inner location, controllingpiling up of the wire turns upon one another. The turns are naturallyspaced farther apart where they pass over the outer circumference of thecore and end caps, and there is no problem of piling up of the wireturns when the inner portions thereof are positioned as notedheretofore. The wire is pressed in against the plates 34 of the end capsas is indicated at 54, and is held in place as by the application of avarnish or the like. The wire in the position where it passes over thethickened rim 42 of the rear end cap 32 is ground down flat to removethe enamel therefrom, and to provide a flat sliding surface for a tapsubsequently to be described.

Three terminals 56, 58 and 60 are aifixed to the insulation 24 inaccordance with conventional practices, being spaced from the ends ofthe winding 40. The opposite ends of the winding are connected to theterminals 56 and 58 for energization of the entire winding. The terminal60 is connected to a tap on the winding adjacent one end thereof, andthe input voltage can be connected to the terminal 60 rather than to theterminal 56, thereby providing a maximum output voltage somewhat higherthan the input voltage. The output voltage is taken from the terminal 58and from a terminal or center lead 62 secured to the rear end cap by thescrew 52. The center lead 62, as may be seen in Figs. 3 and 4 includes astraplike section 64 extending radially along the back of the rear endcap, and extending radially outwardly therefrom. The center lead 62further includes an integral ring section 66 connected by an offset 68to the strap section 64. The ring section 66 is positioned axiallyinward from the end of the core 22 as will be apparent in Fig. 3.

The transformer further includes a molded base 70 of phenolic or thelike plastic. The base, as best may be seen in Figs. 3 and 7, includes agenerally flat front disc 72 having a central recessed portion 74. Thebase is provided on its rear or inner surface with a pair of radiallyspaced lugs 76 adapted to be received in the space between theprojections 46 of the front end cap, and on radially opposite sides ofthe plastic plug therein for positioning the base and the front end caprelative to one another. The rear face of the base plate is providedwith a radial slot or groove 78 adjacent the lugs 76 to provide spacefor a wire leading from the winding 40 to the terminal 60.

The front face of the base is provided with a peripheral recess 80, andwith a central recess 82. A projecting pin or plug 84 extends axiallyfrom the front of the face for non-rotatable association of thetransformer with a mounting plate 86 or the like.

The base 70 further includes a cylinder extending rearwardly from theplate 72 and identified by the numeral 88. The cylinder is provided witha central bore 90 which is countersunk at the rear end at 92. A metalpin 94 extends axiallyinto the countersink 92. The exterior of thecylinder is provided with a chordal flat 96 extending from one end tothe other thereof. The chordal fiat 96 is of considerable importance, asis brought forth immediately hereinafter.

As may be seen in Figs. 3 and the base 70 is assembled with the core 22and associated parts by inserting the cylinder 88 through the bore ofthe core. It will be noted that the bore is somewhat larger than thediameter of the cylinder, and a heat conducting insulating material 98is inserted in this space, and flows partially into the space adjacentthe base plate 72.. Upon hardening the resin holds the parts firmlytogether. The bond is waterproof as will be appreciated. The fiat 96 isof importance in keying the base to the resin, and hence to the core andassociated parts. It is of further importance in that the space betweenthe inner coil winding and the cylinder must be kept reasonably small inorder to provide a sufiicient amount of steel in the transformer, andthis makes flowing of the resin into place rather difficult. The flatprovides an enlarged passageway insuring that the resin will passthrough the space and up against the back of the base plate. It will beobserved that the cylinder terminates short of the rear end cap 3 2, andabuts the ring section 66.

The transformer further includes a shaft assembly 100 best seen in Figs.3 and 4. The shaft assembly includes a mounting sleeve 102 extendingthrough the bore 90 in the cylinder 88 and having at one end a radiallyprojecting flange 104 having a notch 106 therein for receiving the pin94 to prevent rotation of the sleeve relative to the base. A chat washer108, a toothed lock washer 110, and a nut 112 are received on the outerthreaded end 114 of the sleeve 102, all being recessed in the centralrecess at the front of the base plate 72.

The shaft assembly 100 further includes a shaft 116 rotatably receivedin the mounting sleeve 102 and secured against movement into the sleeveby a retaining ring 118 received in a peripheral groove. The front endof the shaft further is provided with a fiat 120 whereby a knob 122 issecured against rotation on the shaft. A set screw 122 is threadedthrough the knob into engagement with the flat 121) to hold the knob onthe shaft.

Rearwardly of the sleeve 102 the shaft 116 is provided with a yoke orstop 124 Welded thereon. The stop further is provided with an integralprojection or tongue 126 engageable wth the pin 94 to limit rotation ofthe shaft 116. As will be apparent, the pin and tongue so limit therotation of the shaft that the sliding tap carried by the shaft does notpass off of the winding at either end.

=Rearwardly of the yoke 124, the shaft 116 is provided with a knob orhead 128 of insulating material, preferably ceramic. The end of theshaft is swaged over as at 130 in a counterbore in the head 128, and thecounterbore preferably is filled with a suitable insulating cement 132.The head 128 is provided at two adjacent corners with relieved sections134 providing shelves 136. At the opposite side, the head is providedwith a projection 138 having tapered sides 140 and a wedge shapedundersurface 142.

The shaft assembly further includes a spring arm 144. The spring arm isprovided with a central aperture at 146 generally complementary to thehead 12.8, including the relieved corners 136, and the wedge-shapedundersurface 142 of the projection 138. The aperture is received overthe shelves 136 and beneath the projection 138, as will be seen in Fig.3. The spring arm is slotted along the opposite sides of the aperture asat 148, the slots angling in at 150, generally in the same shape as theaperture 146. The angled end portions 150 of the slots are connected byan opening 152 providing clearance for a generally Z-shaped limit stop154 welded to the central body formed by the slots 148, 150, and opening152. A notch 156 is provided in the central body adjacent one of theslots 148 to provide clearance for a wire, as will be brought outhereinafter.

An integral spring tongue158, joined to the body, hereinafter identifiedby the numeral 160, adjacent the upper edge thereof (as viewed in Fig.4) is displaced slightly from the plane of the body. Normally, thedisplacement is not sufficient to cause the tongue to engage theZ-shaped limit stop 154, but the limit stop prevents the tongue and bodyfrom being relatively moved a sufficient distance to destroy theresiliency of the spring arm 144. The outer end of the tongue isprovided with depending tabs or flanges 162 forming a brush retainer164. A pair of small struck out fingers 166 is provided on the tonguefor securing a wire as hereinafter will be set forth.

The head 128 is provided with a shank portion 168 having a pair ofdiametrically located splines 170 thereon. These splines are received ina pair of notches 172 of a rotatable slip ring 174. The slip ringengages the previously mentioned ring section 66, the slip rings beingresiliently held together by a coil spring 176 compresses against theslip ring and bearing against the underside of the head 128. The rearsurface of the movable slip ring 174 is provided with an axiallyextending circumferential flange 178 for positively locating the spring176.

A stranded wire 180 is cast or molded into the movable slip ring 174,and is joined at 182 to another stranded wire 184 cast or molded in acarbon brush 1-86. The brush is shaped to provide a narrow surfaceengaging the wire, as is known in this art. The brush is received in thebrush holder 164, and the wires 180 and 184 are isecured beneath thetongue 158 by the struck out fingers 166.

In addition to the parts heretofore enumerated, it will be observed thatthe transformer includes a dial 188 held against the mounting plate 86by a nut 190, the dial being keyed to the transformer by the stud orprojection 84.

As has been indicated heretofore, the body 160 of the spring arm 144 isreceived diagonally across the head 128, being disposed above theshelves 136 and beneath the tapered undersurface 142. This causes theprojecting tongue 158 to hold the brush against the wire winding underspring tension. The Z-shaped stop 154 prevents the tongue from beingbent backwards far enough relative to the body to prevent being sprung."

As will be apparent with particular reference to Fig. 3, the undersideof the head 128 is substantially in the same plane as the outer, grounddown surface of the wire 40 where it passes over the raised rim of therear end plate 32. The shank 168 is actually recessed within thetransformer structure and the semi-recessing of the entire head allows agreater amount of transformer steel to be used in an axial direction,for a given permissible length of the transformer from the front surfaceof the base plate 72 to the rear extremity of the shaft assembly, namelythe outer end of the head 128. Furthermore, with the cementedconstruction, and particularly with the flat on the base cylinder forfacilitating the flow of the resin, only a small space is needed betweenthe core and the cylinder, thus affording a maximum of steel in a radialdirection. As a result, the transformer has a higher current or powerrating than in the transformer.

It is to be understood that the specific form of the invention as hereinshown and described is exemplary only. Various changes in structure willno doubt occur 0 those skilled in the art, and are to be understood asforming a part of this invention insofar as they fall within the spiritand scope of the appended claims.

The invention is claimed as follows:

1. A variable transformer comprising a cylindrical core, a coil windingon said core and insulated thereterminal means connected to saidwinding, a sliding tap engageable with said winding, terminal meansconnected to said tap, a one-piece molded base comprising a cylinder andan integral transverse plate of insulating material, said plate havingan annular recess same side thereof as said cylinder, said cylinderextending through said core with said plate proximate to one end of saidcore, a cementitious material interposed between and bonding togethersaid core and said base, said cementitious material extending into saidrecess, and a shaft assembly extending through said base and carryingsaid sliding tap.

2. A variable transformer as set forth in claim 1 wherein the basecylinder is provided with a chordal flat extending substantially fromend to end thereof and communicating with the plate recess, providingclearance for said cementitious material and further serving to key saidbase through said cementitious material to said core and winding.

3. A variable transformer as set forth in claim 1 wherein the cylinderis provided with a counterbore at the end opposite the plate, andfurther including a metal stop pin mounted in said counterbore andextending axially of said cylinder, said shaft assembly having a stopengageable with said stop pin to limit movement of said sliding tap.

4. A variable transformer comprising a cylindrical iron core, a pair ofinsulating end caps respectively disposed on the opposite ends of saidcore, and each comprising a ring-like plate with a central depressedarea, a coil winding about said core and end caps insulated and a shaftassembly extending through said base and carrying said sliding tap.

5. variable transformer as set forth in claim 4 guides positioning theturns of said winding.

6. A variable transformer as set forth in claim 4 wherein the base plateand the proximate end cap are provided with complementary keying means.

7. A variable transformer comprising a core unit including a cylindricaliron core having a coil winding References Cited in the tile of thispatent UNITED STATES PATENTS ,009,013 Kar'plus July 23, 1935 2,265,666Mekelburg Dec. 9, 1941 FOREIGN PATENTS 607,048 Germany June 29, 1935UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.2,985,857 May 23, 1961 I Fredrick I. Ellin et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent. should read as"corrected below.

Column 2, lines 14 and 15, strike out "the circumference of the cap, Thefront end cap is identical with the rear end cap, but lacks in theinsert 18, a" and insert the same after "from" in line l2 same column 2.

Signed and sealed this 5th day of December 1961.

(SEAL) Attest:

ERNEST w. SWIDER DAVID L. LADD Attesting Officer Commissioner of PatentsUSOOMM-DO- UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo. 2,985,857 May 23, 1961 Fredrick I. Ellin et a1.

It is hereby certified that error appears in the above numbered pat- 5Patent. should reed as ent requiring correction and that the said Letter"corrected below.

strike out "the circumference s identical with the rear end and insertthe same after Column 2, lines 14 and 15, of the cap. The front end capi cap, but lacks in the insert 48, a ".from" in line l2 same column 2.

Signed and sealed this 5th day of December 1961.

' (SEAL) Attest:

DAVID L. LADD Commissioner of Patents ERNEST w. 4SWIDER

